Design of a WT shape

[jdelacruz]

Can someone tell me what LRFD equations i can use for a WT shape subjected to axial and flexure with a lambda exceeding lambda r? Meaning that the shape is slender and must account for web local buckling. I am having trouble specifically finding the right equations especially for Mn to use in the H1-(a),(b) equations.

 

[warrenw]

jdelacruz;
Check out Appendix B section3a."Unstiffened Compression Elements"
Calculate the design strength reduction factor Qs from section 3.a(d) "For stems of tees" using equations A-B5-9 or A-B5-10
Hope this helps
Warren

 

[jdelacruz]

I have seen Appendix B, but I am confused about which limit states to apply and when to use the reduction factor Q. From what I have seen from Appendix F1.7 there are several limiting Mn that are present. I am specifically testing out a WT8x15.5 as a top chord of a truss. Do I use Mn=QFySxc, Equation F1-15 of the specification, etc. I guess I haven't seen a clear roadmap for the M part of H1-1 when you are dealing with a slender WT shape used in a beam column situation. If someone can point me to a clearer road map of what to use as limit states, it would help me out alot. Thanks.

 

[warrenw]

jdelacruz;
Sorry I haven't replied sooner, I was out of town.
As you can see by the lack of replies you have received,this is not an easy question.
This is the way I see it;
The WT8x15.5 is a slender member and must be designed per Appendex "B".
The equations that you are looking at in section F don't apply to this member.
The Design Flexure Strength is determine from Appendix B section 3a. which equals 0.9*Fy*Qs
Therefore the nominal flexural strength (Mn) = Fy*Sx*Qs
The Design Axial Strength (Fc) is determine from Appendix B section 3d equation (A-B5-15)
Therefore the nominal compressive strength (Pn) = Fc.
Now combine these under section H
Like I said, this is how I interpret it.
Warren

 

[jdelacruz]

Thanks. I got the same solution from other sources also. I appreciate your time and effort.